1. Field of the Invention
The present invention generally relates to a structural arrangement enabling substantially constant belt tension to be maintained on a drive belt which encircles and drivingly interconnects a drive pulley or sheave and a driven pulley or sheave in which the center-to-center distance between the pulleys or sheaves is not fixed, that is, one of the sheaves or pulleys can move in relation to the other during operation of the mechanism with which the sheaves and belt are associated. More specifically, the invention relates to the unique mounting of the driven sheave or pulley eccentrically with respect to a rotating shaft having an off-center weight thereon which is driven at a high speed to impart vibratory forces to a structure which supports the shaft, such as an earth compacting device, shaker or the like in which the eccentricity of the eccentrically mounted driven pulley or sheave is offset in the same direction as the off-center weight in order to maintain a more constant center-to-center distance between the sheaves or pulleys and thus maintain a more constant tension on the drive belt.
2. Description of the Prior Art
Many devices utilize off-centered weights that are rotated at high speeds to obtain vibration. Among such devices are shakers, vibratory earth compactors and the like which are usually driven by electric motors, internal combustion engines or the like having a single or multiple groove pulley or sheave on the output shaft that is engaged by one or more V-belts which correspondingly engage a corresponding pulley or sheave on the shaft having the off-center weight mounted thereon or associated therewith. In order to obtain long engine life, the motor or engine is usually mounted on a vibration isolator so that the engine and the drive sheave on the output shaft remains relatively stationary while the driven sheave or pulley on the shaft having the eccentric weight thereon vibrates or moves at a predetermined frequency and amplitude depending upon the particular application or use of the vibratory force. With this arrangement, the center-to-center distance between the pulleys or sheaves changes with the drive belt or belts having to accommodate this variation in center-to-center distance which causes undue stress, premature failure and at times the belts will not stay on the pulleys or sheaves. The following U.S. Pat. Nos. are relevant to this invention.
2,632,334 PA1 2,876,616 PA1 2,994,216 PA1 3,396,988 PA1 3,883,260
Heckner U.S. Pat. No. 3,883,260 utilizes an off-center motor to actually create the vibration which is a different concept from this invention. Austin U.S. Pat. No. 2,876,616 discloses a sprocket 28 which is off-center but this eccentricity creates varying speed on the driven sprocket 25 which is advantageous in the yarn forming industry but is not equivalent to this invention. Morton U.S. Pat. No. 2,994,216 discloses a spring-loaded idler which will retain a substantially constant pressure on the drive belts but is not pertinent to this invention. Kroening U.S. Pat. No. 3,396,988 discloses eccentric sprockets for taking up slack and backlash which is not related to this invention. The other patents mentioned above also fail to disclose any structure equivalent to this invention.